The present invention relates to the field of internal combustion engine control, and, more particularly, relates to the field of control of internal combustion engines in which sensors detect the current values of operating parameters of an internal combustion engine and feed output signals to a control device, which then processes these output signals and on this basis produces control signals which are fed to control devices of the engine.
Conventionally, it is known to provide sensors to an internal combustion engine which detect values associated with different operating parameters of the internal combustion engine, such as, for example, the flow rate of intake air to the engine, the rotational speed of the crankshaft, the operating temperature of the engine, and so forth. In such a system, these sensors produce sensor output signals representative of the detected values, and these sensor output signals are sent to a control device. Based upon the values of these sensor output signals the control device, produces control signals which are sent to control mechanisms of the engine to control various other operating parameters of the engine. For instance, such a control device can control the amount of fuel injected to the combustion chambers of the engine, or the ignition timing of the engine, or the rate of recirculation of exhuast gases to the inlet manifold of the engine.
As a particular example, a Karman vortex flow meter may be used to meter the flow of intake air into the engine inlet manifold. Such a flow meter produces a sensor output signal whose frequency corresponds to the flow rate of intake air. The control device detects the period of the sensor output signal of the Karman vortex flow meter in order to obtain information as to the intake air flow of the engine. This process can be performed in a short time, and is generally sufficiently accurate for operational purposes.
A problem often arises with such a system, however, in that interference or error in the sensor output signal from the sensor can disturb the correct operation of the control device. Such error of the output signal can occur for various reasons, such as electrical interference from the ignition system or the like, disturbance of the sensor by vibration or even by ionizing radiation, or the like. The error in the output signal may consist of a deformed waveform, or even of the absence of one or more control pulses, which, in a frequency-modulated system such as that outlined above, can produce an error which is large in magnitude. The incidence of such errors can be reduced by provision of shielding, filtering, and so on. However, it is impossible to remove them entirely. Such errors may well greatly interfere with smooth control of the engine. For example, in the particular example of a Karman vortex flow meter described above, when one or more peaks of the frequency-modulated sensor output signal are omitted, the amount of intake air provided by the control signal output from the control device may fluctuate wildly. This results in an unacceptable variation of air-fuel ratio provided to cylinders of the engine from the stoichiometric value, with associated problems relating to control of emission of harmful pollutants in the exhaust gases of the internal combustion engine, and/or relating to fuel consumption of the engine.